The present invention relates generally to the magnetic recording of data utilizing thin film transducers and, more particularly to the demagnetization of the yoke in a magnetic recording transducer utilizing a decreasing AC current applied to the write element for a short period of time after the completion of the write cycle.
It is well known that many magnetic recording products take advantage of the improved frequency response and read/write efficiencies provided by thin film ferromagnetic recording transducers. The magnetic elements of the transducer are fabricated from magnetic material deposited in a continuous ferromagnetic film having magnetic remanent states determined by various configurations of the magnetic domains. The transducer magnetic domain configuration is in part determined by the anisotropic characteristics of the transducer yoke material. These anisotropies include effects due to the yoke shape, the material crystalline structure and magnetostriction. The geometric shape of the transducer yokes affects the magnetic domain configuration through the magnetic domain nucleation sites caused by corners and edges or defects in the magnetic material forming the yokes. The stability of the magnetic domain configuration which remains after the write process has saturated the yokes is in part determined by the coercivity of the yoke material and by thermal effects due to resistive heating during writing.
A common problem accompanying the use of thin film magnetic transducers is the occurrence of spurious pulses during data readback immediately following the write process. This problem has been variously termed "popcorn noise", "after-write-drop-in" and "glitch-after-write". These spurious pulses are caused by the decay or relaxation of a metastable non-zero magnetic remanent state to a stable magnetic remanent state which induces a signal in the transducer read/write coil. The relaxation or decay to zero remanence may be initiated by temperature changes in the head or by external stray magnetic fields in the vicinity of the transducer. If the relaxation is not controlled, the pulse may occur during normal reading of data after a write operation. The time of decay or relaxation may be as short as a microsecond or as long as fifty microseconds or more after the completion of a write operation. In order to read back data within a few microseconds of the completion of a write operation, the occurrence of these spurious pulses must be minimized or eliminated.